A gel can be defined as a solution in which the solid, also known as a gelator, is meshed to form a rigid or semi-rigid mixture results. Depending on the structural nature of gel networks, gels can be simply divided into chemical gels and physical gels. In the case of chemical gels, the aggregation units at different levels are connected into three-dimensional networks via covalent bonds whereas in physical gels, the molecules of a gelator aggregate into network structure via various non-covalent interactions, which are considerably weaker than covalent bonds.
Physical gelation of water and solvents include polymers, micro- or nano-particles, and low-molecular mass organic compounds (LMMGs). The gels formed by latter are named supramolecular gels or molecular gels and can be used for gelation of oil from oil-water mixtures for oil spill recovery. The spilled oil is transformed from a liquid into semi-solid or rubber-like materials floating on the surface of water by introducing LMMGs into the oil contaminated water.
Jadhav and co-workers have disclosed a new class of sugargelators that can selectively gel (solidify) the oil phase from an oil-water mixture at room temperature. The process for preparation of gelators is easy and environmentally benign. Further, the gelators can be recovered and reused multiple times (Angew. Chem. Int. Ed. 2010, 49, 7695-7698).
Kar and co-workers have disclosed supramolecular hydrogelation of a composite including single walled nanotubes (SWNTs) and amphiphilic dipeptide carboxylates (Chem. Commun., 2012, 48, 8389-8391).
Kar and co-workers have disclosed dipeptide-based long-chain acids/salts capable of efficiently gelating organic solvents and water. The xerogels prepared from the organogels showed time-dependent adsorption of dyes such as crystal violet (Langmuir 2009, 25(15), 8639-8648).